THE MITES. 



341 



pairs of short-clawed feet. Pentastoma (Fig. 309) occurs in 

 the lungs and liver of man, and in horses and sheep. 



Order 4. Acarina. The mites are degenerate Arach- 

 nida, the body being oval in form, 

 the head usually small, more or 

 less merged with the thorax, while 

 the latter is not differentiated 

 from the abdomen. There is a 

 slight metamorphosis, the mite 

 when first hatched having but 

 three pairs of legs, the fourth 



Fig. 312. Sugar-mite. Much 

 enlarged. 



Fig. 313. Carolina scorpion (Buthus 

 Carolinianus). Natural size. 



'(and last) pair being added after a moult. A typical mite, 

 though above the average size of the members of the group, 

 is the tick (Fig. 310, Ixodes albi- 

 pictus Pack). Closely allied to this is 

 Ixodes lovis Riley, the cattle-tick 

 (Fig. 311), which buries its head in 

 the skin, anchoring itself firmly by 

 means of the backward-pointing teeth 

 of its jaws. Other examples of mites 

 iire the cheese and sugar mites (Fig. 

 312, Tyroglyphus sxccJiari). The lat- 

 ter appear as white specks in sugar, 

 and to them is due the disease known 

 as grocers' itch. Certain mites live Fig. 314. cheiifer cancroi- 



,, . i . .. . , des. Magnified. 



under the epidermis of the leaves of 

 treos, often forming galls. 



